1 Field of the Invention
The present invention relates generally to a semiconductor device. More particularly, the present invention relates to a semiconductor chip package in which an active surface of a semiconductor chip is attached to a bottom surface of a flexible circuit board having a central opening, and in which input/output pads on the active surface of the chip are electrically connected to a circuit layer on a top surface of the flexible circuit board through the opening, so that the package can be reduced to a size on the order of that of the chip.
2 Description of the Prior Art
As semiconductor integrated circuit (IC) chips become increasingly sophisticated, the component density increases as does the number of input/output (I/O) pads per chip, resulting in larger chips. However, there is a continuing need to reduce the size of the semiconductor chip package to meet the need for smaller devices.
One of the packages that has been developed to meet this need is a ball grid array (BGA) package. The BGA package provides a relatively high surface-mount density and improved electrical performance as compared to a conventional plastic package. A distinct difference in the structure of the BGA package from the conventional plastic package is that the electrical interconnection between the semiconductor chip and a mother board is provided by a printed circuit board (PCB) having circuit patterns and solder balls instead of a lead frame.
The typical BGA package 10 is illustrated in FIG. 1. As shown in FIG. 1, the chip 11 is attached to the top surface of the PCB 12. The circuit patterns 13 on the top surface of the PCB 12 extend to the bottom surface through vias 15. The circuit patterns 13 on the top surface are electrically connected to the chip 11 by bonding wires 14, while those on the bottom surface are electrically connected to the mother board (not shown) by solder balls 16. Parts of the top surface of the PCB 12, the chip 11, and the bonding wires 14 are encapsulated by resin 17. The body of the PCB 12 is generally made of FR-4, FR-5, or BT (Bismaleimide triazine) resin. FR-4 and FR-5 are fire retardant epoxy glass-reinforced laminates.
The BGA package 10 is larger than the chip 11 because the PCB 12 used in the BGA package 10 requires an area without circuit patterns 13 to allow the chip 11 to be attached to the PCB 12. Furthermore, the width and the distance between adjacent circuit patterns 13 are limited to 70 .mu.m, respectively. Therefore, it is difficult to manufacture a BGA package when circuit patterns 13 having a small width or a small degree of spacing there between are required.